Precipitating size with chromium and aluminum salts



Patented Jan. 19, 1954 PRECIPITATING SIZE WITH CHROMIUM AND ALUMINUMSALTS Raymond C. McQuiston, West Newton, and Frank E. Davenport, NewtonCenter, Mass, assignors to Minnesota Mining & Manufacturing Company, St.Paul, Minn., a corporation of Delaware No Drawing. Application January6, 1947, Serial No. 720,480

4 Claims.

This invention relates to aqueous fibro-colloidal dispersions, methodsof preparation, and products made therefrom.

An object of the invention is to produce stable dispersions of fiberswherein each fiber has an adsorbed coating of colloidal binder particleswhich have been deposited from an initial colloidal dispersion thereofby a procedure involving a correlated utilization of aluminum andchromic salts coupled with a shifting and control of pH values.

Such dispersions are to be distinguished from mixed dispersions such asresult when a dispersion of fibers is mixed with a dispersion ofcolloidal particles but without the latter becoming bound to thesurfaces of the former.

The invention provides aqueous fibre-colloidal dispersions which areadapted to be sheeted and dewatered with little or no loss of thecolloidal binder material in the white water (i. e. in the water whichis separated from the coated fibers), to provide highly coherentfinished sheet materials of excellent strength and toughness, includingpapers of various types. The sheeting may be formed on paper-makingmachines.

A great variety of fibers and of colloidal binder materials may beutilized to produce sheet materials having different properties adaptedfor many different uses. Use may be made of rubber latex (natural orsynthetic) to produce tough,

rubbery sheet materials; and a feature of the invention is that highproportions of such rubber may be incorporated.

An object is to provide stable dispersions of paper-making fibers inwhich the fibers are coated with latex particles of natural or syntheticrubber (elastomer polymers), or plastic polymers. Such latex particleshave a highly coa gulative propensity, and a feature of the presentinvention is These dispersions may be prepared in large scale batches ina beater and then processed on commercial paper-making equipment toproduce novel types of paper. Use can be made of cylinder machines,Fourdrinier machines, and wet machines. In this connection it isemphasized that laboratory experiment procedures quite commonly fail towork out satisfactorily when transferred to the paper mill. The presentinvention provides procedures which are adapted for use in regularfull-scale commercial operations.

An object is to produce pliable unified papers containing highproportions of natural or synthetic rubber (30-l50% or more), which arefinethe ability to handle such materials.

grained and highly uniform and homogeneous; which have a remarkabledensity, toughnessand resiliency; which have a high wet-strength andwhich are impermeable to various solvent materials (depending on thenature of the particular rubber employed); and in which the fibers areso firmly held and unified that the paper cannot be split or delaminatednor the fibers be pulled loose at the surfaces. Creped papers can bemade by creping the paper stock prior to completion of the normalpaper-making operation, while still in a moist condition. An object isto produce unified papers which can be employed as the backings forpressure-sensitive adhesive tapes (such as masking tapes, shoe tapes andelectrical tapes), baokings for waterproof abrasive sheets in the natureof sand-'- paper, and as gasket sheeting, package and containersheeting, artificial leather, etc., making possible products havingnovel and valuable properties not heretofore obtainable. The paper canbe coated during the making procedure by ap-. plying a coatingcomposition at a calender stack.

The invention has a wide field of application,

mosetting resin materials can be used, alone or in combination withrubbers. Proteins (such as casein and glue) can be used. Colloidalcoloring agents can be included. The dispersions of this invention maybe employed in making relatively thick sheetings, such as floorcoverings,

and stiff leather-like sheets useful for shoe midsoles and inner solesand in making luggage, etc.

Dispersions may also be made for use as coating compositions andcements.

A feature of the present invention is that the technique permits ofincluding a suspension of finely divided non-colloidal particles in theaqueous dispersion (as illustrated by zinc oxide and other pigments andfillers, and by sulphur vulcanizing agents, for example). Properpeptization of the non-colloidal suspensoid is maintained so that itdoes not adversely affect the dispersed state of the colloidal particlesprior to deposition nor the deposition thereof on the fibers.

Such suspensoid is retained and carried into the final dewatered sheetas a uniform mix distributed throughout the fibre-colloidal phase. Atub-sizing procedure can be used for incorporating impregnants into thesheet during the making operation.

The character of the final sheet can be modified by heating and bysubjecting to the action of solvents, with or without pressing orcalendering, depending upon the nature of the binder material employed.

The present invention is based upon our discovery of the controlleddeposition effects which can be produced by a properly correlatedconjoint use of a soluble aluminum salt (such as aluminum sulphate), anda soluble chromic salt (such as chromic sulphate), when coupled with aprojerly controlled shifting of pH'values. Other examples of suchaluminum and chromic salts are aluminum chloride, aluminum nitrate,basic chromic sulphate, chromic chloride, and chromic nitrate. These areall trivalent salts of strong acids. The chromic salts have theso-called coordination type of structure. v

The problem is to cause the dispersed binder particles to be graduallyadsorbed upon the fiber surfaces; so that a system of mixed colloidalparticles and fibers, dispersed in water, is trans formed into a systemin which the fibers are coated with adsorbed binder particles whileremaining stably dispersed in the water. The great difiiculty is thatthis transformation must be accomplished without causing a coagulativecollapse of the system resulting in large curds or lumps of particles(which may include fibers), which are not deposited on the free fibersand cannot be redisbursed due to the irreversible nature of the,colloidal system. This complex electro-colloidal system is delicate andextremely sensitive to adverse influences, and it is unfortunately truethat the very agents which are effective in producing deposition of thecolloidal particles upon the fibers are also capable of causingcoagulation. Hence the problem cannot be solved by the mere use ofcoagulating agents. The problem is especially acuate when it isattempted to use large proportions of irreversibly coagulative colloidalbinder particles and to substantially entirely deposit them upon thefibers.

The fibers and the colloidal binder particles each areelectro-negatively charged in a mixed dispersion in water, and hencenormally repel each other. The present invention provides a way ofintroducing electro-positive particles into the system which areselectively attracted to the surfaces of the fibers and in turn attractand hold the negatively charged colloidal binder particles. Thus thebinder particles become coated upon and bound to the fibers by what maybe termed an electrostatic cement. A difiiculty which had to be overcomewas that if the positively charged electrostatic cement particles shouldprematurely discharge the negatively charged dispersed binder particles,then the latter would coagulate or agglomerate without being depositedproperly upon the fibers.

The aluminum and chromium salts which We employ are individually capableof producing strong positive ions or particles in aqueous solutions,which have a pronounced precipitating action on dispersed colloids. Butneither one alone produces the desired results, especially'under theconditions necessarily encountered when working with large batches andwith highly coagulative colloids, in respect to the fibre-colloidal typeof system with which we are concerned. The conjoint use which we make ofthese two types of compounds does not involve a mere additive orcomplementary action, since there is an interaction whereby the efiectof each is modified or altered. By way of background to an understandingof our invention, is is desirable to point out the following factsconcerning these compounds.

The aluminum salt (such as aluminum sulpha't'e)v produces varioushydrolytic and ionic products when put into water, depending on theacid-alkaline condition prevailing. (This condition is most convenientlyexpressed in terms of the pH value of the solution. The pH scale goesfrom 0 to 14, with a pH of 7 indicating a neutral condition, lowervalues an increasingly acid condition, and higher values an increasinglyalkaline condition.) At pH values of 4.0 to 6.0, aluminum sulphate (forexample) interacts with water to produce positively charged hydrated alumina particles having the formula:

(A1203A12H20) n which can be adsorbed on the negatively-charged fibersto act as an electrostatic cement for precipitating and retaining thecolloidal binder particles. Increase of the pl-I value leads to adiiierent type of charged alumina which is not effective for the desiredcementing action. Further increase of the pH value to above 10.0,results in the alumina becoming largely converted to a negativelycharged aluminate. When the pH value is depressed below 4.0, less ofthe'desirable electrostatic cement alumina is available, as it revertsto aluminum sulphate which is ionized to form positive aluminum ions(Al+++) instead of hydrolyzing to form the positive alumina particles.The pl-I value which exists depends in part on the concentration ofaluminum sulphate which is introduced into the water, since it is anacidic material, and in part on whatever other substances are introducedwhich exert an acidifying or alkalizing action. Thus sulphuric acid canbe used for acidifying and sodium hydroxide for alkalizing.

The aluminum salt is most eflective in providing an electrostatic cementaction when the pH value is within the range of 4.0 to 6.0; the optimumpH value being approximately 4.8 to 5.2, at which the strongestelectropositive potentials are produced.

When the readily coagulative colloids, such as rubber latex, are presentit is 'difiicult to avoid sudden coagulation thereof when positive ionsor particles are introduced. This is especially true when working withlarge batches, due to the substantial time factor involved beforeintroduced substances can become uniformly distributed by mixing so asto have the intended concentration, and due to other efiects. Hence thedifliculty of merely using the aluminum salt in attempting to producethe results aimed at by us, owing to'its strong propensity to causecoagulation and to cause rapid deposition.

The water-soluble chromium co-ordination salts, such as chromicsulphate, provide charged chromium nuclei having valuable properties inthe present connection. In accordance with Werners theory, the positivechromium ion of each molecule is surrounded by six co-ordinative groups,the whole constituting an ionic nucleus having an electrostatic charge,outside of which are located the remaining radicals or ions of themolecule, which are oppositely chargedand held by the primaryelectrostatic valence forces.

aqueous solution, the aforesaid chromium nucleus constitutes a largecharged ion, consisting of the central chromium ion surrounded by its6-co-ordinative groups, which may beiHzO or anion groups. A givennucleus can be altered by penetration of one or more anions whichdisplace the H or anion groups previously present, and in this way thecharge of an electropositive nucleus can be reduced and it can even bemade electronegative. The penetrating ion may be either an outer ion ofthe chromium compound itself, or may be supplied by some other compoundpresent in the solution. The modification of the charged chromiumnucleus, and its consequential modification of its environment, arecaused or influenced by various conditions, in-

cluding the acidity or alkalinity of the solution, I

etc.

An enlarged chain type of charged chromium nucleus can be produced bypenetration of hydroxyl ions which link together adjoiningfchromium ions(a process called olification) The chromium sulphates lend themselvesparticularly to the formation of positively charged, stable, complexchain structures, which have the greatest elecoropositive potentialwithin the pH range of 4.8 to 5.2. At pH values below 4.8, sulphate ionscan penetrate the nucleus and displace H2O groups, and this can even becarried to the point of producing a negative nuclear ion.

The chromic salt is most effective in providing an electrostatic cemenaction when the pH value is within the range of 4.0 to 6.0, the optimumpH value being approximately 4.8 to 5.2.

Thus it is evident that the presence of charged chromium nuclei canprofoundly influence the ionic and electric properties of a solution,the functioning of other compounds present, and the state offibro-colloidal dispersions therein, and that the effect is a functionof the pH value and of other substances present. That is why, in regardto the present invention, it has been stated that the aluminum andchromic deposition salts act in a conjoint fashion which is not merelyadditive or complementary. The positively charged chromium nuclei per secan act as a so-called electrostatic cement, but conjoint use with thealuminum salt is necessary to produce the results we desire.

A method of making stable fibro-colloidal dispersions, in accordancewith this invention, will now be described in a step-by-step mannerwhich includes a discussion of the principles involved; to be followedby the detailed description of illustrative examples. It is obviouslyimpossible to set forth specific detailed directions for all possiblefibro-colloidal systems; but it is possible to analyze the basicprocedure and indicate the governing principles so that those skilled inthe art will be able to practice the invention generally, makingwhatever adjustments are necessitated by any particular situation.

First stage Second stage The dispersed fibers are preferably conditionedby adding a small proportion of the chromic salt to provideelectropositive chromium nuclei, and preferably also a small proportionof the aluminum salt, especially when a paper-making stock is beingprepared. These may be added in dry form or in solution form. Thus equalparts by weight of chromic sulphate and aluminum sulphate may be added,in amount which produces an acid pH value in the range of approximately4.0 to 6.0. The aluminum salt may be omitted, but in such case the finalwhite water may not be so clear. The result of this stage is to causeadsorption of positive particles (serving as an electrostatic cement) onthe fiber surfaces so that they will be preconditioned to a certainextent before the binder colloid is introduced. However, this is done toa limited extent only, to avoid undue flocculation or agglomeration ofthe binder colloid when introduced. This stage is an optional one and isnot needed when the subsequent stages are performed in substantiallyoptimum fashion.

Third stage An alkalizing agent is added, such as sodium or potassiumhydroxide, or sodium or potassium silicate, for the purpose of shiftingthe pH value to a strongly alkaline value which will inactivat thecoagulative propensity of the aluminum and chromium deposition agentsemployed in the process. The pH value should be raised to above 10.0 andpreferably to 10.5-11.0 or higher. When an alkali-metal silicate is usedin whole or in part as the alkalizing agent, colloidal hydrated silicamay be formed and, in any event, the deposited binder colloid willcontain adsorbed silica which will thus be incorporated in the finaldewatered sheet. Its presence in the sheet will impart desirableproperties for certain purposes, such as increased resistance topenetration by organophilic oils and solvents, especially when theproportion (SiOz basis) is at least 5% by weight of the fibers. Acomplex of fiber-adsorbed latex particles and silica has novelproperties as compared to the properties resulting when the silica isomited. When a strong alkali, such a sodium hydroxide is used, it may bereplaced in part by an alkaline buffer salt of a strong base and a weakacid, such as di-sodium phosphate.

Fourth stage A dispersion of the binder colloid is added and thoroughlydistributed. For example, this may be in the form of a latex of naturalor synthetic rubber, containing a mildly alkaline stabilizing agent.Thus the synthetic rubber latex as obtained from the producing plant,may contain a soap; and natural rubber latex may contain ammonia. Theproportion employed depends upon the kind of sheeting or coatingultimately desired. The present invention permits of incorporatingextremely large amounts, for example the binder solids may exceed of thefiber solids. The method permits of admixing a suspension ofnoncolloidal particles without adverse results. For example, asuspension of zinc oxide can be introduced as a filler or pigment.Vulcanizing agents can be introduced when a vulcanizable binder is used,so as to be present if the ultimate sheet is to be vulcanized.

,A protein protective colloid is preferably-incorporated to prevent theformation of small curds and to impart smoothness to the fibrous slurry,especially when large proportions of co agulative binder colloid areintroducedi' A type" which forms slowly and finely divided 'precip--itatable systems is best adapted to the present method. The gamma formof soybean protein (such as Prosein) has been found to be highlysuitable. Casein can be used. Only a small proportion is needed. This isintroduced as an alkaline dispersion in water, and is added directly tothe fibrous slurry, preferably after the binder colloid has beenadmixed.

Fifth stage A small additional proportion of the chromic salt (such aschrcmic sulphate) is added to the slurry, which is thoroughly mixed. Itfunctions in part as an adsorption retardant for the alu- The aluminumsalt (such as aluminum sulphate) is added to the alkaline slurry insuificient amount to cause the deposition of the binder colloid upon thefibers. The greater the amount of the binder colloid, the greater thamount of electrostatic cement needed to attract and bond the colloidalparticles to the fibers. The pH is adjusted to an acid value within therange of 4.0-6.0. The optimum value is approximately 4.8 to 5.2. Thealuminum salt also serves for adjusting the pH value due to itsacidifying nature. The acidifying eiiect depends upon the ccncentrationof the aluminum salt, which involves the amount of the aluminum saltrelative to the amount of Water present. An acid (such as sulphuricacid) can be added to produce the desired pH value if the amount of thealuminum salt employed is insufficient. If the desired amount of thesalt results in too low a pH value, an alkaliZing' agent can be added toraise the pH to the desired value. Because of the previous steps in theprocess, including the incorporation of the chromium nuclei in thepreceding stage, this introduction of the aluminum salt results in anexcellent deposition of the colloidal binder particles upon the fibersina controlled manner which avoids coagulation and substantial formationof undeposited lumps or fioccules.

and is adapted for forming dewatered sheets having the advantageouscharacteristics previously mentioned, with little or no loss of bindercolloid material in the white water.

If the dispersion is diluted with water (which tends to raise the pHvalue), an acidifying agent should preferably be added to hold the pHvalue in the desired range, so as to prevent the colloidal binderparticles from sluffing ofi from the fibers.

Aqueous dispersions of positively-charged binder and peptizing colloidsmay be added to the fibro-colloidal dispersion; for example, dispersionsof melamine hydrochloride, urea resins, etc.

In the case of leather fibers which are either initially in the form ofchrome leather or are chromiurn-collagenated in situ in the dispersion,it is necessary to employ an excess of the chromic salt so as toprovide.free inorganic chromium nuclei forthe purposes herein required. 'In thecase of. vegetable-tanned leather fibers, a much The resultant Ifibre-colloidal dispersion is stable and smooth 01? *a-vulcanizing agentcomposition, known as larger proportion of chromic salt is required thanin the case of cellulose fibers (or even in the case of chrome-tannedleather fibers) as such vegetable-tanned leather fibers are verystrongly charged negatively and tannic acid is present which adverselyeffects the desired result. In this case his necessary to cause chromiumions to combine With carboxyl groups of the proteolytic fiber to enablea deposition of positiv charges or particles on the surfaces of saidfibers by means of the inorganic chromium nuclei. This process consumesa part of the total of the chromic salt, and hence a greater amount isneeded in order to furnish the necessary free chromium nuclei.

If animal glue is used as the binder colloid,

7 alone or in combination with another binder colloid, it is desirableto employ tannic acid and sodium chloride to produce precipitation ofthe glue as a glue tannate (glycine tannate), which provides negativelycharged particles capable of effective deposition on the fibers by meansof the chromium and aluminum compounds.

The following examples set forth procedures which we have successfullyused in a paper mill for preparing beater stocks subsequently formedinto highly unified and uniform papers or sheets having a high contentof synthetic rubber. The descriptions of the beater treatment procedureare divided into six parts corresponding to the six stages previouslydiscussed.

Example 1 (1) The beater was loaded with the required amount of waterand was then-charged with 800 lbs. (dry weight basis) of a semi-bleachedkraft paper-making pulp (a sulphate type of pulp). Water was again addedand the pulp was given a hard heating for eight hours, resulting in apulp slurry containing about 3% of fiber pulp (dry Weight basis). The pHvalue was 7.80. This pH value is subject to variation dependent on thepulp and on the pH value of the water used.

(2) There Was then added 24 lbs. of commercial chromic sulphate and 24lbs. of commercial aluminum sulphate (known as paper makers alum). Theweights given are for the commercial salts, which are hydrates. Thechromic sulphate has the formula: Cr2(SO4)s-xI-IzO, and is a hydratedmixture containing about 27% E20 by weight. The aluminum sulphate hasthe formula: Al2(s.O4)3 -18H2O. The salts were predissolved in smallportions of water and added as 25% solutions to the slurry, andthoroughly mixed in for about 20 minutes. The resultant pH value was4.10.

. (3) There was next mixed in 2'70 lbs. of a 38% by weight solution ofsodium silicate having an SiOz to Na2O ratio of 3.25. The sodiumsilicate solids amounted to 12.8% of the cellulose paper stock (dryweight basis), thus providing 9.6% of SiOz relative to the paper fibers.Mixing was continued for about 20 minutes, and the resultant pH valuewas 10.10.

(4) The synthetic rubber latex was then introduced and thoroughly mixedfor about 20 minutes. This consisted of 1,450 lbs. of GRS No. 3,produced according to U. S. Government specifications in a RubberReserve Corporation plant. This rubber is a co-polymer of 50% butadieneand 50% styrene (commonly known as Buna-S type rubber). This latexcontains about 2% rosin soap as a dispersant. I The latex contains 38%rubber solids, which amount to 68.9% of the cellulose paper stock.

There was next mixed in 87 lbs. (dry weight) Gr-3" (sold by R. T.Vanderbilt Co., Inc., of New York city), containing sulphur, butylzimate as an acceleraton'zinc oxide as an activator, hydroquinonemono-benzyl-ether as an antioxidant, and. a small amount of casein andalkali as dispersants, which composition is ground in water to form adispersion having a solids content of 52%. This vulcanizing compositioncan be omitted if it is not desired to vulcanize the synthetic rubber inthe ultimate paper.

There was next mixed in a dispersion of gamma soybean protein. Use wasmade of Prosein (sold by the Glidden Company). The dispersion consistedof lbs. of-Prosein, '75 lbs of water, and lb. of caustic soda. Thisprovided protein in the proportion of 1.9% of the cellulose paper stock.About minutes of mixing was employed to insure that the batch wasthoroughly mixed before the next step.

The resultant pH value was 10.20

(5) There was next mixed in 24 lbs. of chromic sulphate, predissolved inwater to form a 25% solution. The slurry was thoroughly stirred forabout 20 minutes. The resultant pH value was 9.60 and the slurry wasready for the final introduction of aluminum sulphate to deposit therubber particles of the latex upon the cellulose fibres.

'(6) There was then slowly added 140 lbs. of aluminum sulphate,predissolved in water as a 25% solution, over a period of about 20minutes, with mixing. The resultant pH value was 4.20. The slurry wasfurther mixed and the colloidal rubber particles gradually deposited onthe fibres, until deposition was completed andthe white water was clear,requiring about 15 minutes.

The resultant dispersion was stable, and it was found that it was inbetter condition for paper making after aging for four or five days thanit was initially.

Microscopic examination of the dispersion made clearly visible thedeposition of the latex particles upon the outer surfaces of the tubularcellulose fibers and showed that but little had agglomerated to formseparate clumps or bundles of rubber. These latter had a size no greaterthan the order of magnitude of the fiber diameters, but weresufliciently large so that they would be mechanically retained in thefibrous sheet formed in paper making, rather than passing 01f in thewhite water. V

The total proportions of the chief ingredients can be summarized asfollows, being expressed in percentage by weight relative to thecellulose paper fibers:

Kraft pulp (dry basis) Synthetic rubber (solids) Aluminum Sulphate(hydrate) The foregoing beater slurry dispersion was formed into papersof various ream weights using a regular cylinder machine type of papermachine. The slurry was pumped from the heater to a beater chest, withaddition of water in the usual way to reducethe consistency and aid inthe transfer, which raised the pH value; and was then transferred to amachine chest. Just priorto reaching the paper machine, the slurry wasmixed with a large amount of water in a mixing box so cylinder vats (atthe wet end of the machine where the pulp is dewatered and formed intosheets) was reduced to a paper-making consistthat the slurry arriving inthe l0 ency of 0.5% (percentage by weight of the coated fibers). At thispoint the pI-I value was 6.8 (the added water raising the valueaboutthat which existed at the end of the beater treatment). A lower valuewould be desirable and can be ob tained by adding acid or a concentratedsolution of aluminum sulphate to the slurry at the mixing box, or byoperating a closed system in which the white water is recycled fordiluting the beater slurry; and this would also permit employment of ahigher pI-I value in the last stage of the beater treatment. Suchprocedures enable the attaining of a pH value of approximately 4.8 to5.2 both in the beater and in the cylinder vats, producing a stillbetter deposition and bonding on the fibers and less tendency of theadsorbed latex particles to slufl' off into the'white water. Thecylinder molds were of 60 mesh (but in subsequent work it was found thatthe mesh size worked. better in minimizing loss of material into thewhite water). The paper was produced at the rate of 70 ft. per minute.It contacted the dryer cylinders for about 5 minutes and was subjectedto a temperature of about 220 F., thus causing vulcanization of therubber phase (which probably was completed thereafter at roomtemperature). The dried paper was subjected to cold calendering.

Example 2 This example illustrates a procedure similar to that of thepreceding example, chiefly differing in the use of a latex of anacrylate polymer. Hence the description will be given more briefly.

(1) and (2) These steps were the same as in Example 1. The resultant pHvalue was 4.30 in this case.

(3) 355 pounds of sodium silicate (38% solution) was added lbs. ofsodium silicate solids). The resultant pH value was 10.40.

(4) The acrylate polymer latex dispersion consisted of a mixture of twokinds, namely, polyisobutyl acrylate latex (28% solids), andpolymethyl-isobutyl acrylate latex (30% solids). 765 lbs. of the formerand 1,420 lbs. of the latter were used, providing a total of 640 lbs. ofacrylate polymer solids (amounting to 80% of the cellulose paper stock).In this case the protein protective colloid was not added at this point,but subsequently as hereafter described. The resultant pH value was10.40. 0

(5) '40 lbs. of chromic sulphate was added, followed by 48 lbs. of gammasoybean protein dispersed in alkaline solution (as described in Example1), and then 16 lbs. of additional chromic sulphate. After thoroughmixing, the resultant pH value was 9.70.

(6) Aluminum sulphate, predissolved in water, was gradually added, withmixing, in amount sufiicient to result in a pH value of 5.0.

Example 3 This example also illustrates a procedure similar to that ofExample 1, chiefly differing in the use of a Buna-N type of syntheticrubber.

(1) and (2) These steps were the same as in Example 1. .The resultant pHvalue was 3.95 in this case. g

(3) Sodium silicate was added in sufficient amount to produce a pH valueof 10.25 (252 lbs. of 38% solution).

(4) There was first added 1,400 lbs. of Hycar O R-15 latex containing40% by weight of rubber solids. This is a Buna-N type of syntheticrubber formed of the copolymer of butadiene and acrylonitrile in theratio of 60:40, and is sold by the B. F. Goodrich Chemical Company,Cleveland, Ohio. There was next added 15 lbs. of Prosein, dispersed inalkaline solution as described in Example 1. Following this there wasadded 23.5 lbs. (solid weight) of the dispersed G-B vulcanizercomposition described in Example 1. The pH value after each of theseadditions was 10.23.

24 lbs. of chromic sulphate was mixed in, resulting in a pH of 9.75. i

(6 150 lbs. of aluminum sulphate was added, producing a pH ofapproximately 4.0.

Example 4 This example illustrates the preparation of a stock which wasformed into innersoling and midsoling (useful in making shoes) on a wetmachine type of paper machine. The procedure was similar to that forExample 1.

(1) and (2) These steps were the same as in Example 1, except that only8 lbs. of each of the salts were used. The resultant pH value was 4.62.

(3) 162 lbs. of a 38% sodium silicate solution (61.5 lbs. of solids) wasused to produce a pH value of 10.08.

(4) 450 lbs. of GRS No. 3 synthetic rubber latex (38% solids) was usedand 8.5 lbs. (dry weight basis) of the 6-1-3 vulcanizing composition.There was next mixed in 7.5 lbs. of the Prosein protein in dispersedform and 1 lb. of sodium hydroxide, resulting in a pH value of 10.30.

(5) There was next added 10 lbs. or" watersoluble dye material adaptedto produce a tan color in the final sheeting. 10 lbs. of chromicsulphate was added, resulting in a pH value of 9.98. The'dye wasset onthe paper fibers by the salts, acting as mordants.

(6) 65 lbs. of aluminum sulphate was added and the resultant pH valuewas 4.28.

The slurry was transferred to the wet machine in the usual way and wassheeted out to form, upon drying and calendering, stifi leather-likesheets useful as innersoling and midsoling of shoes.

Example 5 (1) and (2) The procedure was the same as in Example 1.

(3) 252 lbs. of a 38% sodium silicate solution (96 lbs. of solids) wasused and resulted in a pH value of 10.5 in this case.

(4) 1,450 lbs. of GRS No. 3 synthetic rubber latex (38% solids) and 26.5lbs. (dry weight basis) of the G-3 vulcanizing composition were used,followed by the addition of lbs. of.

Prosein protein in dispersed form, resulting in a pH value of 10.53.

(5) 24 lbs. of chromic sulphate was added, resulting in a pH value of10.04.

(6) 125 lbs. of aluminum sulphate was added, resulting in a pH value of4.0 in the beater.

In this example the transfer of the stock to the cylinder machine(described in connection with Example 1), involved adding sufiicientaluminum sulphate (as a 25% solution) to the stock in the mixing box tobring about a pH value of 4.8 at the vat where the fibers are dewatered.This overcame the tendency of the added water to raise the pH value toan undesirably high value after the slurry leaves the beater. Thisprocedure resulted in the fibro colloidal dispersion being at theoptimum pH value at the time of dewatering to make paper, and therebyinsured the best bonding of the rubber particles upon the cellulosefibers and minimized any tendency of the particles to slufi off into thewhite water.

Among the papers made. from this stock was a creped paper having thefollowing physical properties: a caliper thickness of 6.0 mils (0.0060inch), a lengthwise tensile strength of 12.1 lbs. for a inch width teststrip, a crosswise tensile strength of 5.0 lbs. per inch width, 9.length wise stretch of 20%, and a crosswise stretch of 29 Example 6 Inthis example the beater procedure was similar to that described inconnection with the preceding examples except that the sodium silicatewas entirely replaced by sodium hydroxide as the alkalizing agent. Thischange resulted in a much softer type ofpaper.

(1) and (2) 700 lbs. (dry weight basis) of the paper-making pulp wasused, and 21 lbs. each of chromic and aluminum sulphates, resulting in apH value of 3.70.

(3) 18 lbs. of sodium hydroxide was used to raise the pH value tosomewhat over 11.00. Y

(4) 1,350 lbs. of GRS No. 3 synthetic rubber latex (38% solids) and 23lbs. (dry weight basis) of the G-3 vulcanizing composition were used,followed by the addition of 1 3 lbs. of Prosein protein in dispersed rorm. Thev pH value was still somewhat over 11.00.

(5) 21 lbs. of chromic'siilpliat was added.

(6) A total of 55 lbs. of alui'ninum sulphate was added, resulting in apH value of 4.4 in the beater.

As explained in connection with Example 5, additional aluminum sulphatewas added in the mixing box to attain a pH value of 4.8 in the stock atthe paper-making stage.

Among the papers made from this stock was a creped paper having acaliper thickness of 5.3 mi1s., lengthwise and crosswise tensilestrengths of 4.2 and 3.9 lbs, respectively (for /2 inch width teststrips), and lengthwise and crosswise stretch valuesof 20%. A flatuncreped paper was also made which had a caliper of 3.9 mils, lengthwiseand crosswise tensile strengths of 10.0 and 4.0 lbs., respectively, andlengthwise and crosswise stretch values of 4% and 12%, respectively.

Example 7 g This example illustrates the use of an exceptionally highproportion of synthetic polymer solids, and the use of beaten glassinepaper scrap as the fiber stock. The protein protective colloid wasomitted. Sodium hydroxide was used as the alkalizing agent. There wasobtained a smoothsurfaced, rubbery, translucent sheeting impermeable tooils, water andmoisture vapor.

(1) 700 lbs. of white glassine paper scrap was charged into the beater.Glassine paper is transparent and the fibers are extremely short due tothe degrading efiect' of the treatment employed in making thepaperstock. The scrap was given eight: hours of hard beating whichfurther reduced the fibers.

2) 21 lbs. each r chromic and aluminum sifili'aplgates were added,resulting in a pH value 0 (3) 21 lbs. of sodium hydroxide was added.resulting in a pH value of 10.9.

(4) The synthetic latexintroduced consisted of 2,545 lbs. of GeonPlastic Latex (55% solids), Which supplied. 1,400.1bs. of solids (200%b3v 13 weight of the paper fibers). This material is an aqueousdispersion of a copolymer of vinyl chloride anda minor proportion ofvinylidene chloride, which is-plasticized with dioctyl phthalate in theproportion by weight of 2 parts polymer and 1 part plasticizer. Eachparticle contains its ownicontent of polymer and plasticizer. ThisGeon.synthetic latex is sold by the B. F. Goodrich Chemical (30.,Cleveland, Ohio.

(5) 21 lbs. of chromic sulphate was added.

(6) 80 lbs. of aluminum sulphate was added, resulting in a pH value of4.0. In order to increase the pH value to more nearly the optimum, therewas added 14 lbs. of sodium silicate, resulting in a pH value of 4.4.

As explained in connection with Example 5, additional aluminum sulphatewas added in the mixing box to attain a pH value of 4.8 at thepaper-making stage. The stock was processed on a cylinder machine andresulted in rubbery, pliable, smooth-surfaced, translucent sheeting. Thetransparency and smoothness is increased by hard calendering using hotrolls. Maximum transparency can be obtained by using a latex polymerphase which has an index of refraction substantially identical to thatof the cellulose fibers.

Example 8 This example illustrates the use of a mixed dispersion ofsynthetic rubber ltex and a rubbertackifying resin having a strongadhesion to cellulose fibers, which results in depositing upon thefibers a mixture of rubber particles and compatible resin particlescapable of blending together to form a rubber-resin flux.

(1) and (2) 700 lbs. of kraft paper-making pulp was used and was given ahard beating for 8 hours; followed by the addition of 21 lbs. each ofthe chromic and aluminum sulphates.

(3) 223 lbs. of a 38% sodium silicate solution (85 lbs. of solids) wasused and resulted in a pH value of 11.1.

(4) 1000 lbs. of GRS No. 3 synthetic rubber latex (380 lbs. rubbersolids), followed by 18.6 lbs. (dry weight basis) of the G-3 vulcanizingcomposition, were added. There was also added 245 lbs. of an aqueousdispersion of pentaerythritol ester of rosin (98 lbs. solids), obtainedfrom Hercules Powder Co., followed by the addition of '7 lbs. of Proseinprotein in dispersed form.

(5) and (6) 21 lbs. of chromic sulphate was added, followed by theaddition of 120 lbs. of aluminum sulphate, resulting in a pH value of4.3 in the beater.

As explained in connection with Example 5, additional aluminum sulphatewas added in the mixing box to attain a pH value of 4.8 in the stock atthe paper-making stage. The stock ran excellently on the cylindermachine and the paper, while still moist, was creped. The resultingunified creped paper was used in making pressure-sensitive masking tape.

As a variation of the foregoing procedure, in another experiment use wasmade of a dispersed plasticizer, namely, 123 lbs. of an aqueousdispersion of hydrogenated methyl ester of rosin (49 lbs. solids),obtained from Hercules Powder Co. The proportion of the aqueousdispersion of pentaerythritol ester of rosin was reduced to 123 lbs. (49lbs. solids). The procedure was otherwise the same and resulted in astock which ran excellently on the machine.

Example!) a I This example illustrates the preparation of a stock formaking a tough wrapping and packaging paper containing both syntheticrubber and asphalt.

(1) and (2) Kraft paper cuttings in 'the amount of 700 lbs. were givenahard beating for 3 hours; followed by the addition of 10.5 lbs. each ofthechromic and aluminum sulphates. I v (3) 111 lbs. of a 38% sodiumsilicate solution (42 lbs. of solids) was addedand resulted in a pHvalue of 10.0. Then 3 lbs of sodium hydroxide was added to raise the pHvalue to 10.7.

(4) 140 lbs. of an aqueous dispersion of a soft asphalt (84 lbs. solids)was incorporated, followed by 445 lbs. of GRS-No; 3 synthetic rubberlatex (167 lbs. rubber solids), and 7.3 lbs. (dry weight basis) of theG-3 vulcanizing composition. There was also added 7 lbs. of "Proseinprotein in dispersed form.

(5) and (6) 21 lbs/of chromic sulphate was added, followed by theaddition of lbs. of aluminum sulphate, resulting in a pH value of 3.9.

Additional aluminum sulphate was added to attain a pH value of 4.8 inthe stock at the papermaking stage. This stock handled excellently onthe cylinder machine.

Having described various embodiments of our invention for purposes ofillustration, rather than limitation, what we claim is as follows:

1. A method of preparing an aqueous fibrocolloidal slurry adapted foruse in making unified sheet material on a paper-making machine,comprising the steps of (1) dispersing cellulose paper-making fibers inwater to form a fibrous slurry, (2) conditioning the fibers byintroducing small proportions of chromic sulphate and aluminum sulphate,(3) alkalizing the slurry to a pH value in the range of 10.0 to about11.0, (4) admixing a colloidal binder polymer latex, (5) introducing asmall additional proportion of chromic sulphate, the amounts of saltsthus far introduced being insufiicient to deposit the latex particlesupon the fibers, (6) introducing aluminum sulphate in sufiicient amountto deposit the latex particles upon the fibers and adjusting the pHvalue to approximately 4.8-5.2.

2. A method of making unified paper having a high rubber content,adapted for use in commercial paper mills, comprising the steps of: (1)beating cellulose fibers in water to form a paper-making beater slurry,(2) conditioning the fibers by introducing small proportions of chromicsulphate and aluminum sulphate, (3) alkalizing the slurry to a pH valuein the range of 10.0 to about 11.0, (4) admixing a rubber latex having asolids weight of at least 30% of the dry weight of the fibers, (5)introducing a small additional proportion of chromic sulphate, theamount of salts thus far introduced being insufficient to deposit thelatex particles upon the fibers but sumcient to cause a controlleddeposition without coagulation in the next step, (6) introducingaluminum sulphate in sufiicient amount to deposit the latex particlesupon the fibers and adjusting the pH value to 4.0-6.0, and allowingdeposition to be completed so that the white water is cleared, ('7)diluting the resulting fibro-colloidal slurry with water to papermakingconsistency and acidifying to secure a pH value of approximately 4.8-5.2at the papermaking stage, (8) dewatering the slurry and forming paper ona paper-making machine, the

13 white water being" clear" and substantially free from latex.

3 A, method according to-claim' 2 wherein an alkali-metal silicate isemployed for alkalizing instep (3), in sufficient. amount. to provide atleast 5% by weight of S102 relative to the cellu lose fibers.

i 4-. A method according to. claim 2; wherein a. dispersion ofa proteinprotective colloid, is incorporated after the introduction of the latexand priortothe; final introduction: of the aluminum. sulphate.

RAYMOND-C. M'CQUISTQNJ FRANK DAVENPORT;

Reierencesl Cited in the file of thispatent- UNITED STATESPATENTS.

Number Name Date 1,939,996 Rose et a1. Jan. 5-, 1992 1,943,943 CarnieFeb. 9, 1932 1,992,599 Tucker et al.' Feb. 26,1935

Numbei Name Date 1,993,277 Murpnyet a1; a Mar.- 5, 1935 2,112,5 1? CableMar. 29',- 1938 2,330,084 Scott; sept.- 21, 1943 FOREIGN PATENTS NumberCountry Date 14,753 Great- Britain flnrehh of 1890 12,299 Great Britainof I891 28,219 Great Britain as of 1909 OTHER REFERENCES India RubberWorld, February 1, 1923, pp. 283-284. I p H Kaye: Year Book 1922-23Institute Rubber Industry, pp. 1-15.

Ers'pamer: Technical Assoc. Pulp and Paper Industry Papers, SeriesXXITI", pp. 132-137,}940.

Manufacture of, Pulp and Paper, 3d, edition, v01. IV, sec 5', pp. 18 and19, published by MGiaw-Hill, New York ("1938).

1. A METHOD OF PREPARING AN AQUEOUS FIBROCOLLOIDAL SLURRY ADAPTED FORUSE IN MAKING UNIFIED SHEET MATERIAL ON A PAPER-MAKING MACHINE,COMPRISING THE STEPS OF: (1) DISPERSING CELLULOSE PAPER-MAKING FIBERS INWATER TO FORM A FIBROUS SLURRY, (2) CONDITIONING THE FIBERS BYINTRODUCING SMALL PROPORTIONS OF CHROMIC SULPHATE AND ALUMINUM SULPHATE,(3) ALKALIZING THE SLURRY TO A PH VALUE IN THE RANGE OF 10.0 TO ABOUT11.0, (4) ADMIXING A COLLOIDAL BINDER POLYMER LATEX, (5) INTRODUCING ASMALL ADDITIONAL PROPORTION OF CHROMIC SULPHATE, THE AMOUNTS OF SALTSTHUS FAR INTRODUCED BEING INSUFFICIENT TO DEPOSIT THE LATEX PARTICLESUPON THE FIBERS, (6) INTRODUCING ALUMINUM SULPHATE IN SUFFICIENT AMOUNTTO DEPOSIT THE LATEX PARTICLES UPON THE FIBERS AND ADJUSTING THE PHVALUE TO APPROXIMATELY 4.8-5.2.